This application is directed to sheet or paper handling apparatus, particularly rollers for orienting paper in a printing apparatus such as a photocopier, printer, or the like. More particularly, this application is directed to using one or more pneumatic rollers having openings through which air can either be expelled or drawn, i.e., pressure or vacuum, to direct and handle the paper. The invention will be described with reference to a printing apparatus, however, it will be appreciated that the invention has broader applications and may be advantageously employed in other related environments and applications.
In conventional printing apparatus, sheet material or paper is handled by a series of rollers and counter rollers. A counter roller is required to generate forces normal to the tangential surface of a roller for handling the sheet. Counter rollers, unfortunately, lead to jams, paper tears, wrinkling, or other surface damage to the sheet. Aside from the undesired physical damage to the paper, it also requires service or maintenance and additional space is needed to allow access by service personnel to eliminate the jams.
Paper handling also typically requires a component of motion perpendicular to the direction of the roller motion, for example for paper registration. This cannot be accomplished with a standard set of rollers (a roller and counter roller). Instead, an additional set of rollers is required that release and grab the sheet. This unnecessarily adds to the cost, complexity, and the length of the paper path. Moreover, all this complexity is ultimately less reliable and at odds with the goal of reducing the space required to handle the paper.
Still another concern with paper handling in a printing apparatus is the ability to transition between different rates of speed in the paper path. As will be appreciated, in known printing apparatus a sheet of paper undergoes numerous velocity accelerations and decelerations as it passes through the processing path. For example, a paper sheet proceeds from a stationary position at the supply, is increased in velocity to a first workstation, is decelerated at the first workstation, subsequently accelerated to a downstream or second workstation, decelerated at the second workstation, etc. Individual handling and increased processing are goals that require the paper sheets to be spaced apart as far as possible.
On the other hand, increasing the spacing necessarily increases the velocity transitions of the paper. This, in turn, requires the rollers to continuously accelerate and decelerate to perform the velocity transitions or paper bending. The forces associated with the acceleration and deceleration place great stress on the roller and the associated motor systems. Additionally, the increased acceleration and deceleration require still further space in the assembly.
The general use of air in either a pressure or vacuum arrangement associated with a roller assembly is known in the art. By way of example, U.S. Pat. Nos. 4,493,548; Re. 32,541; 4,062,538; 4,543,160; 4,726,502; 4,792,249; 4,997,178; 5,032,875; 5,127,329; 5,197,812; 5,401,721; 5,431,384; 5,299,411; and 5,411,245 are representative prior art patents that generally relate to roller assemblies. These known arrangements, however, have not adequately addressed system demands for increased speed of processing, space constraints, handling different paper stock, and varying rates of speed in the paper path.